[Amps] Kenwood TL-922 soaring bias current in SSB Mode ?

[Posselt Werner]

Hello!
 
I have (again) a problem with a TL-922.
In CW (lower HV) on any band in TX mode without any drive power applied
the grid current keeps steadily on the preset value by the Zener Diode.
While in SSB mode where the Zener is bypassed IG starts soaring after a
few seconds and it would not stop unitl TXing is interrupted.
Any hints what has to be done to cure this problem?
Is this oscillation caused by the increased HV in SSB mode?
 
Thanks for your help!
 
Werner / OE2WPO